This invention relates to an aqueous pigmented color ink set and to the use thereof in ink jet printers.
Ink jet printing is a non-impact method that in response to a digital signal produces droplets of ink that are deposited on a substrate such as paper or transparent film. Ink jet printing has found broad application in industry as well as for output from personal computers in the office and the home. There are several classes of ink jet printer, for instance thermal drop-on-demand printers, piezo drop-on-demand printers, and continuous ink jet printers.
Ink jet printers, particularly those for use in the home or office, generally use aqueous inks, and such inks commonly employ dyes as colorants. For multi-color printing utilizing the subtractive primary colors it is common to provide three or four separate inks comprising a yellow ink, a magenta ink, a cyan ink, and optionally a black ink. However the use of ink sets comprising more than four colors is known. For example M. Waters in American Ink Maker, November 1988, describes a process in which an increase in color gamut of 50% is achieved by using a six-color dyed ink set compared with a four-color dyed ink set, and U.S. Pat. No. 5,734,800 describes the preparation of a six-color ink set using dye-based inks, some of which may also contain fluorescing agents. It was shown that use of a six-color process system enabled reproduction of a greater range of colors than use of a four-color process system.
The correct choice of dyes for use in such inks is important for good color gamut and image quality. The book xe2x80x9cThe permanence and care of color photographsxe2x80x9d by H. G. Wilhelm published in 1993 by Preservation Publishing Company, Grinnell, Iowa describes on pages 91 and 92 that color imbalance is usually a more important criterion for determining the usable display lifetime of prints than neutral fading. Thus although good lightfastness of the dyes used in ink jet printing is important, it is also important that all the dyes fade at roughly the same rate, because changes in color balance are more readily detectable by eye than an even fading of all colors. For instance U.S. Pat. No. 5,858,075 discloses a dye set useful for ink jet inks comprising a particular combination of yellow, magenta, and cyan dyes. Images produced with the dye set disclosed in U.S. Pat. No. 5,858,075 have lightfast characteristics necessary to preserve the trueness of the inkjet images by (1) producing images having less light fade and (2) images that when they do fade, fade in a more uniform manner across the color set. There is considerable interest in the use of pigmented inks for ink jet printing. The term pigment describes a colorant, which is substantially insoluble in the aqueous ink medium. Various classes of pigment are catalogued and classified in the Pigments and Solvent Dyes section of the Colour Index International, published by the Society of Dyers and Colourists in 1997, and there are additionally numerous other insoluble colored compounds which are not included in the Colour Index. It is expected that pigmented inks will display improved fastness to washing and weathering of the prints produced and better light stability on outdoor exposure than those based on other colorants. However it is well known that it is difficult to match the color gamut of a dye-based ink set with pigmented inks.
European Patent Application 0 933 406 A discloses the use of a six-color ink set in which the colorants are cyan, magenta, yellow, green, orange and black pigments. The orange pigment is selected from CI Pigment Orange 43 and/or 36, the green pigment is selected from CI Pigment Green 7 and/or 36, the blue pigment is CI Pigment Blue 15:3, the magenta pigment is CI Pigment Red 122, 202, or 209, the yellow pigment is selected from CI Pigment Yellow 109, 110, 74 or 138, and the black pigment is Carbon Black. The use of additional pigmented inks, namely orange and/or green inks, achieves color reproduction equal to dye-based inks.
A need still exists for a pigmented ink set with extended color gamut for multicolor ink jet printing which will print successfully through an ink jet printer to provide good quality images of excellent light stability which fade in a more uniform manner when exposed to light and provides excellent color gamut, without introducing other disadvantages.
We have devised a pigmented color ink set which is particularly suitable for ink jet use.
In the present invention, these purposes, as well as others which will be apparent, are achieved generally by providing a pigmented aqueous ink set which comprises:
(a) a cyan ink which comprises at least one pigment which is a phthalocyanine compound;
(b) a magenta ink which comprises at least one pigment which is a quinacridone compound;
(c) a yellow ink wherein the pigment is C.I. Pigment Yellow 155;
(d) a green ink wherein the pigment is selected from the group consisting of C.I. Pigment Green 7, 36, and mixtures thereof;
(e) an orange ink wherein the pigment is selected from the group consisting of C.I. Pigment Orange 34, 36, 43, 61, 64, or 71, and mixtures thereof; together with optionally
(f) a black ink which comprises a black pigment.
Preferably there is also present at least one water soluble organic cosolvent. The pigmented ink set is suitable for use in ink jet printing. Other objects, features, and advantages of the present invention will become apparent from the following detailed description of the invention when considered with reference to the drawings, as follows: